An ambitious, but intriguing, possibility for radically increasing the availability and adequacy of health care, while containing its cost, is to use the computer as a consultant to augment and extend the skills of all health care providers. We propose to pursue a program of fundamental research in representation of knowledge, decision-making, problem-solving, program explanation and clinical cognition, to understand how to construct computer programs that, as an integral part of the health care system, can amplify the knowledge and reasoning powers of medical decision-makers. We plan to apply the techniques so developed to problems in the diagnosis and therapy of acid/base and electrolyte disturbances, diagnosis of birth defects using an existing data base of diseases and associated manifestations, the development of multi-modal cancer therapy protocols, and the application of the methods of decision analysis to produce general tools for physicians to use in analyzing difficult clinical cases.